Modern trends in power engineering are characterized by a tendency towards an ever increasing level of the operating voltage of electrotechnical devices such as power transmission lines, transformers and generators, which helps increase their efficiency figure.
However, an increase of the operating voltage level for electrical machines poses the problem of developing novel designs of their windings whose insulation would be capable of operating under conditions of elevated voltage. In particular, an increase of generator voltage raises the problem of developing a high-voltage stator winding employing, for example, high-voltage stator coils.
The prototype to the disclosed technical solution is found in a stator coil of a high-voltage generator (cf., G. N. Aleksandrov, V. L. Ivanov, K. P. Kadomskaya, N. A. Kozyrev, M. V. Kostenko, G. S. Kuchinskii, I. F. Polovoi, B. M. Rayab, V. A. Hoberg "Tekhnika vysokikh napriazhenii"--High Voltage Technology, Vyschaiya Shkola Publishers, Moscow, 1973, pp. 456-457).
The stator coil of a high-voltage generator comprises an electrical lead-in made of an electrically conductive material and coupled electrically to the beginning of the first turn of the coil. The coil turns made of conductive material are coated with several layers of turn-to-turn insulation with a screen layer applied on top, while the turn-to-turn insulation and the screen layer of each subsequent turn, starting with the first turn, envelop all the preceding turns.
In the prior art design of a stator coil of a high-voltage generator, insulation cones formed by insulation layers adjoining the electrical lead-in are characterized by their large size. Said prior art stator coil of a high-voltage generator lacks reliability in operation, which hampers the manufacture of generators rated for high voltages of the stator winding (110 kV, 220 kV and above). The prior art design of the stator coil of a high-voltage generator does not permit of direct cooling of the stator winding.
Large overall dimensions of the stator coil of a high-voltage generator are due to the fact that in the zone where the insulation continuity may be disturbed, i.e., in the zone of the electrical lead-in and insulation cones adjoining the latter, the electric field distribution is non-uniform which may lead to an insulation on breakdown. In order to eliminate this risk, the insulation layers and screen layers applied on top of the latter form insulation cones whose length is proportional to the need of reducing the electric field intensity to a preset value, which results in a great length of each insulation cone increasing sharply with the growth of rated voltage.